Aromatic polyester resins have long been known. For instance, p-hydroxy benzoic acid homopolymer and copolymers have been provided in the past and are commercially available. Those aromatic polyesters normally encountered in the prior art have tended to be somewhat intractable in nature and to present substantial difficulties if one attempts to melt process the same while employing conventional melt processing procedures. Such polymers commonly are crystalline in nature, relatively high melting or possess a decomposition temperature which is below the melting point, and when molten frequently exhibit an isotropic melt phase. Molding techniques such as compression molding or sintering may be utilized with such materials; however, injection molding, melt spinning, etc., commonly have not been viable alternatives or when attempted commonly have been accomplished with difficulty. Such polymers commonly cannot be melt extruded to form nondegraded fibers. Even those aromatic polymers which exhibit a melting point below their decomposition temperature commonly melt at such high temperatures that quality fibers may not be melt spun. For instance, fibers melt extruded at extremely high temperatures commonly possess a voidy internal structure and diminished tensile properties.
Representative publications which discuss aromatic polyesters include: (a) Polyesters of Hydroxybenzoic Acids, by Russell Gilkey and John R. Caldwell, J. of Applied Polymer Sci., Vol. II, Pages 198 to 202 (1959), (b) Polyarylates (Polyesters from Aromatic Dicarboxylic Acids and Bisphenols), by G. Bier, Polymer, Vol. 15, Pages 527 to 535 (August 1974), (c) Aromatic Polyester Plastics, by S. G. Cottis, Modern Plastics, Pages 62 to 63 (July 1975), and (d) Poly (p-Oxybenzoyl Systems): Homopolymer for Coatings: Copolymers for Compression and Injection Molding, by Roger S. Storm and Steve G. Cottis, Coatings Plast. Preprint, Vol. 34, No. 1, Pages 194 to 197 (April 1974). See also, U.S. Pat. Nos. 3,039,994; 3,169,121; 3,321,437; 3,553,167; 3,637,595; 3,651,014; 3,723,388; 3,759,870; 3,767,621; 3,778,410; 3,787,370; 3,790,528; 3,829,406; 3,890,256; and 3,975,487.
It more recently has been disclosed that certain polyesters may be formed which exhibit melt anisotropy. See for instance, (a) Polyester X7G-A Self Reinforced Thermoplastic, by W. J. Jackson, Jr., H. F. Kuhfuss, and T. F. Gray, Jr., 30th Anniversary Technical Conference, 1975 Reinforced Plastics/Composites Institute, The Society of the Plastics Industry, Inc., Section 17-D, Pages 1 to 4, (b) Belgian Pat. Nos. 828,935 and 828,936, (c) Dutch Pat. No. 7505551, (d) West German Pat. Nos. 2520819, 2520820, 2834535, 2834536, and 2834537, (e) Japanese Pat. Nos. 43-233, 2132-116, 3017-692, and 3021-293, (f) U.K. Patent Application No. 2,002,404, and (g) U.S. Pat. Nos. 3,991,013; 3,991,014; 4,066,620; 4,067,852; 4,075,262; 4,083,829; 4,118,372; 4,130,545; 4,153,779; 4,156,070; 4,159,365; 4,161,470; and 4,169,933. See also commonly assigned U.S. Ser. Nos. 877,917, filed Feb. 15, 1978 and now U.S. Pat. No. 4,184,996, issued Jan. 22, 1980; 10,392, filed Feb. 8, 1979 and now U.S. Pat. No. 4,238,599 issued Dec. 9, 1980; 10,393, filed Feb. 8, 1979 and now U.S. Pat. No. 4,238,598, issued Dec. 9, 1980; 17,007, filed Mar. 2, 1979 and now U.S. Pat. No. 4,230,817, issued Oct. 28, 1980; 21,050, filed Mar. 16, 1979 and now U.S. Pat. No. 4,224,433, issued Sept. 23, 1980; 32,086, filed Apr. 23, 1979 and now U.S. Pat. No. 4,219,461, issued Aug. 26, 1980; and 54,049, filed July 2, 1979.
Additionally, it is known that a variety of polymers can be prepared which possess the recurring unit: ##STR1## For example, U.S. Pat. Nos. 3,501,444 and 3,697,478 describe aromatic azopolymers containing amide linkages that are prepared by an oxidative coupling technique. The described azopolymers may be processed into fibers, films, and other shaped articles. U.S. Pat. No. 3,639,340 discloses thermostable polymers which are prepared by the polycondensation of a phenol or a polyphenol with a dianhydride having a generic formula which includes azophthalic and azoxyphthalic acids. The polymers may be used to form molded articles, laminates and varnishes. U.S. Pat. No. 3,966,678 relates to a multicellular synthetic polymer which is prepared by the reaction of maleic anhydride and a polyaldimine. The polyaldimine has an extensive generic formula which encompasses the product of such reactants as 4,4'-diamino-azobenzene and 4-formylazobenzene. The formed multicellular polymer is stated as being effective as an insulating material. Heterochain polyesters derived from 4,4'-azobenzenedicarboxylic acid are described in Chemical Abstracts, Vol. 62, 13252e (1965). Similar heterochain polyesters derived from 3,3'-azobenzene-dicarboxylic acid are described in Chemical Abstracts, Vol. 63, 687b (1975). In both abstracts, the formed polyesters are formulated into films. Although prior art of the type discussed in this paragraph discloses various polymers containing the azobenzene group, the search has continued for high strength, high modulus, low melting point polymers which may be processed into fibers, films and other types of shaped articles. This invention was developed as a result of that search.
It is an object of the present invention to provide a wholly aromatic polyester capable of forming an anisotropic melt which is derived from 4-hydroxy-4'-carboxy azobenzene.
It is an object of the present invention to provide an anisotropic wholly aromatic polyester derived from 4-hydroxy-4'-carboxy azobenzene which may be melt processed into fibers, films and other types of shaped articles.
It is an object of the present invention to provide a process for preparing a wholly aromatic polyester capable of forming an anisotropic melt which is derived from 4-hydroxy-4'-carboxy azobenzene by melt polymerizing the esterified monomers.
It is another object of the present invention to provide an anisotropic wholly aromatic polyester derived from 4-hydroxy-4'-carboxy azobenzene which may readily be melt processed into fibers, films, or three-dimensional shaped articles.
It is a further object of the present invention to provide an anisotropic wholly aromatic polyester derived from 4-hydroxy-4'-carboxy azobenzene which may be melt extruded to form fibers of a relatively high modulus of elasticity.
These and other objects, as well as the scope, nature and utilization of the invention will be apparent to those of ordinary skill in the art from the following detailed description and appended claims.